Direct recruitment of N-myc to target gene promoters.

Abstract

The N-myc gene is amplified in 20-25% of human neuroblastomas, and this amplification serves as a poor prognostic factor. However, few genes have been determined to be direct targets of N-myc. Our current studies focused on identifying N-myc target genes, especially those affected in cells such as neuroblastomas that have high levels of N-myc protein. To pursue this goal, we performed differential expression screens with cell-culture systems containing high versus low levels of N-myc. The design of our experiments was such that we should identify genes both upregulated and downregulated by N-myc. Accordingly, we identified 22 genes upregulated by N-myc and one gene downregulated by N-myc. However, only five of these genes responded to increased N-myc levels in more than one system. Further analysis of the regulation of these genes required determining whether they were direct or indirect targets of N-myc. Therefore, we used a formaldehyde crosslinking and immunoprecipitation procedure to determine whether N-myc was bound to the promoters of these putative target genes in living cells. We found that low levels of N-myc were bound to the promoters of the telomerase and prothymosin genes in neuroblastoma cells having low amounts of N-myc but that the amounts of N-myc bound to these promoters greatly increased with overexpression of N-myc. However, the amount of max bound to the promoters was high before and after induction of N-myc. Therefore, our studies suggest that N-myc competes with other max partners for binding to target promoters. Our use of the chromatin immunoprecipitation assay suggests a molecular explanation for the consequences of amplification of the N-myc gene in neuroblastomas.

• Authors: S M Mac, C A D'Cunha, P J Farnham
• Journal: Molecular carcinogenesis (Mol Carcinog) Vol. 29 Issue 2 Pg. 76-86 (Oct 2000) ISSN: 0899-1987 [Print] United States
• PMID: 11074604 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Proto-Oncogene Proteins c-myc
• RNA, Messenger

Topics

• Cell Line
• Fibroblasts (metabolism, physiology)
• Gene Expression Profiling
• Gene Expression Regulation, Neoplastic
• Genes, myc
• Humans
• Neuroblastoma (genetics, metabolism)
• Oligonucleotide Array Sequence Analysis
• Promoter Regions, Genetic (genetics, physiology)
• Proto-Oncogene Proteins c-myc (genetics, metabolism, physiology)
• RNA, Messenger (biosynthesis, genetics)
• Reverse Transcriptase Polymerase Chain Reaction
• Skin (cytology)
• Transcriptional Activation (physiology)